His family was from Ding Prefecture (定州, in modern Baoding, Hebei), but it is (based on his father's career) unclear whether he was born there.
Feng Meng was described to be intelligent but wicked, and he gained the favor of Li Siyuan's powerful chief of staff An Chonghui, and was eventually promoted to be the deputy defender of Yedu (鄴都, in modern Handan, Hebei).
[7] As the empress' brother, Feng Yu's power also rose quickly, as he became Zhongshu Sheren (中書舍人) and became in charge of drafting imperial edicts.
Apparently in short order, he became the military prefect (團練使, Tuanlianshi) of Ying Prefecture (潁州, in modern Fuyang, Anhui),[5] and then quickly promoted to be imperial scholar at Duanming Hall and deputy minister of census (戶部侍郎, Hubu Shilang), becoming often involved in Shi's policy-decision process.
It was said that because he was particularly capable of pleasing the emperor, he became even more powerful, such that on an occasion when he was on leave due to illness, Shi stated to the other chancellors, "For all posts that are at the prefect level or greater, wait until Feng Yu returned to fill them."
Feng used the emperor's trust for personal benefit, such that those who wanted posts all went to his mansion to bribe him, leading to a degradation of the Later Jin governance.
Feng and Li Song (who was by this point also chief of staff) believed the rumors, and had Shi Chonggui's uncle-by-marriage Du Wei the military governor of Tianxiong Circuit (天雄, headquartered in modern Handan, Hebei), write to Zhao to further entice him.
At Emperor Taizong's instruction, Zhao wrote back to "confirm" his intention to do so, in order to set a trap for Later Jin forces.
[9] When Emperor Taizong sent the former Later Jin general Zhang Yanze into Kaifeng first to accept the surrender, the soldiers pillaged Feng's mansion and took much of the massive wealth that he had accumulated.
Among the Later Jin officials ordered to be part of Shi's train were Zhao Ying, Feng Yu, and Li Yantao.